The present invention concerns the manufacture of elastic casings as supports used inside tires to support the load in the event of a puncture or blowout. More precisely, it concerns the production of supports which have at the base a substantially inextensible belt made of reinforcing wires of the type normally used to reinforce tires.
Patent application EP 0,796,747 describes a particular example of such a support. In FIG. 1 of said application EP 0,796,747, it can be seen that the base 10 of the support is reinforced by wires 11 arranged substantially at zero degree with respect to a plane perpendicular to the axis of rotation of the support.
In this application, the term xe2x80x9cwirexe2x80x9d covers both mono and multifilaments, or an assembly, such as cables, cords or actually any type of equivalent assembly, regardless of the material and treatment of these wires, for example, surface treatment or sheathing or presizing to promote adherence to the rubber. The term xe2x80x9czero degreexe2x80x9d refers to an angle measured with respect to the circumferential direction, in other words, with respect to a plane perpendicular to the axis of rotation of the support (an xe2x80x9cequatorial planexe2x80x9d), thus observing the usual conventions for tires. The angle is said to be xe2x80x9csubstantiallyxe2x80x9d equivalent to zero degree because the reinforcement that makes it possible to oppose centrifugation of the support is accomplished by the winding of a wire or bead strip of parallel wires with a certain installation pitch, so that the angle is not zero degree in the strict sense of the term, but it is in practice at least locally slightly greater than zero degree in order to be able to sweep the entire desired width.
A suitable material for making such a support is rubber.
Different techniques are known for manufacturing a molded object: compression molding, transfer molding, injection molding. Compression molding presupposes the introduction of the volume of rubber needed inside the mold before closing it, whereas transfer molding and injection molding both assume that the mold will be closed prior to introduction of the volume of rubber required in the mold. The choice is a function specifically of the proposed production runs, with injection molding, while more expensive in terms of initial investment, having a lower marginal cost and permitting more uniform pressure and temperature of the material during the vulcanizing reaction, and making it possible to achieve a higher geometric quality.
But injection, as well as transfer, molding do not lend themselves to non-homogeneous products reinforced by flexible reinforcements. In particular, these processes, entailing the introduction of material into a closed mold, are poorly adapted when the reinforcement is a ply of wires because the wires do not stay put, or stay put very poorly, in the mold. The rubber pressed down into the mold brings the wires with it when it fills the mold. It therefore poses a major problem in assuring a precise positioning of the wires in the vulcanized support. This is why the process of pressing rubber into a closed mold for wire-reinforced rubber parts is not used. For example, it is well known that the tires are not injected; first, a rough blank is made that is rather close to the final form of tire to be manufactured, the blank including reinforcing wires inserted at the design point between the different layers of rubber; then the molding is done by closing the necessary molding components around the blank.
An object of the invention is a support such as described in patent application EP 0,796,747 that can be made by pressing material down into a previously closed mold, while ensuring that the position of the reinforcing wires desired by the designer of the support is fully respected.
The safety support according to the invention is intended to be mounted on a tire rim of a vehicle. The support includes an axis of rotation, a base defined by a substantially cylindrical radially internal face designed to be mounted around the rim, and a body forming the support attached to the base. The base includes a set of substantially inextensible circumferential reinforcing wires sheathed in an elastomer material. The support is made by injection under pressure into a closed cavity through feed points arranged on the body of the support. This support is characterized in that the base includes supplementary reinforcing elements arranged, at least in part, radially and externally relative to all the circumferential reinforcing wires and axially with respect to the feed points.
Preferably, the supplementary reinforcing elements include reinforcing wires oriented at an angle xcex1 equal to or greater than 60 degrees relative to the circumferential direction.
The supplementary reinforcing elements contain the movements of the circumferential reinforcing wires during the pressurized injection into the mold cavity. It is these supplementary elements that first come into contact with the injection front of the material in the cavity. Since this front is substantially in the same axial plane, the orientation of the reinforcing wires at an angle xcex1 greater than 60 degrees relative to the circumferential direction enables them to resist any shifting induced by this injection front. Consequently, the position of the circumferential reinforcing wires arranged under the supplementary reinforcing elements is also maintained in the desired position by the designer of the support.
It should be noted that these supplementary reinforcing elements play no functional role for the support during operation. Their role is limited to facilitating the creation of supports whose circumferential reinforcing wires are arranged according to the wishes of the designer of the support.
In a first embodiment, the feed points being substantially arranged in the same equatorial plane, substantially in the center portion of the support body, the supplementary reinforcements extend axially over a length 2L equal to or greater than one-third of the axial width of the support base. The axial extension of the supplementary reinforcing elements is preferably limited to one-half the base of the support.
In a second embodiment, the feed points being substantially arranged in the same equatorial plane on one side of said support, the supplementary reinforcements surround the axial end of the set of circumferential reinforcing wires on the support side and extend axially and externally relative to all the circumferential reinforcing wires over a length L equal to or greater than 10 mm. Preferably, L is equal to or less than 30 mm.
In the latter case, it has been found that a length L of less than 10 mm was insufficient to limit efficiently the movements of the circumferential reinforcing wires due to the entrainment phenomenon linked to the injection front of the material injected during the pressurized injection into the mold. On the other hand, over 30 mm in length, the effect is practically always similar. This would add to the cost and weight of the support without producing any improvement in the precision of placement of the circumferential wires.
The nature of the supplementary reinforcing wires can be very varied. One may use a twilled fabric or two plies with wires oriented along +xcex1 and xe2x88x92xcex1. It is also possible to have a single ply with wires oriented at an angle xcex1 equal to or greater than 80 degrees and preferably 90 degrees.
In the context of this invention, the term support will cover a support, an accessory designed to be mounted inside a tire to give it a temporary operating mode at zero pressure, a non-pneumatic casing designed to be used alone in normal service, with adaptations as to choice of component materials and/or design of the object itself not being the purpose of this patent application. In other words, this invention can find application regardless of the precise destination of the item, and is not limited to a particular design of the molded object, provided it is reinforced by wires, nor to a particular material, provided it can be achieved by pressurized injection into a closed cavity.